1. Field of the Invention
The invention relates to brushless motor systems for vehicle fuel pumps.
2. Discussion
In a conventional DC motor, stationary brushes contact a set of electrical terminals on a rotating commutator. This contact forms an electrical circuit between a DC electrical source and armature coil-windings. The brushes and commutator form a set of electrical switches, each firing in sequence. Electrical power flows through the armature coil closest to the stator.
Conventional fuel pumps for E-85 fuel, i.e., a mixture of up to 85% fuel ethanol and gasoline by volume, include brushed DC motors. Brushes of these motors are susceptible to electrochemical deposition of ions when operating in E-85 fuel. This electrochemical deposition increases the resistance of the motor, which may slow the armature speed, resulting in a reduction of the flow rate of the pump.
A brushless DC motor is an AC synchronous electric motor. Permanent magnets of a rotor rotate relative to a wound stator. An electronic controller distributes power via a solid-state circuit. As power passes through the windings, the induced magnetic field in the windings reacts with the field in the rotor to create mechanical rotation. This mechanical rotation is harnessed via an impeller and pumping chamber in a fuel pump to create desired hydraulic pressure and flow.
Conventional neodymium compression bonded ring magnets used in brushless DC motors soften and come apart when submerged in E-85 fuel. This may result in a locked rotor condition of the motor.
Slot fill is a measure of the percentage of open space of a cross section of a lamination which is filled with copper windings. Conventional winding techniques require thicker wires to achieve desired stator resistance. These thicker wires limit achievable slot fill because the wires bow out from the lamination during winding.